RESUMO

Staphylococcus aureus is recognized worldwide as one of the main contagious mastitis agents in cattle and can express a set of antimicrobial resistance genes and virulence-associated genes that explain the wide range of outcomes of intramammary infections. Staphylococcus aureus strains are heterogeneous: their different resistance and virulence patterns, associated with host-level factors and treatment factors, are related to the severity of infection. The aim of this study was to determine phenotypic antibiotic susceptibility, occurrence of selected antimicrobial resistance genes and other virulence genes in 93 S. aureus strains isolated from clinical mastitis in 6 countries: Argentina, Brazil, Germany, Italy, the United States (New York State), and South Africa. These isolates were tested against a total of 16 drugs (amoxicillin-clavulanate, ampicillin, cefazolin, cefoperazone, cefquinome, enrofloxacin, erythromycin, gentamicin, kanamycin, lincomycin, oxacillin, penicillin, rifampin, spiramycin, sulfamethoxazole/trimethoprim, tylosin) by minimum inhibitory concentration (MIC) assay, and examined for the presence of 6 antibiotic-resistance genes (blaZ, mecA, mecC, ermA, ermB, ermC) and 6 virulence-associated genes (scn, chp, sak, hla, hlb, sea) via PCR analysis. The phenotypic results of this study revealed the presence of 19.4% penicillin-resistant strains, whereas 22.6% of the strains were classified as having resistance (5.4%) or intermediate resistance (17.2%) to erythromycin. Most (96.8%) of the isolates were inhibited by cephalosporins, and all were susceptible to amoxicillin-clavulanate. Two strains (1 from Germany, 1 from Italy) were resistant to oxacillin and were positive for mecA. Among the other antimicrobial resistance genes, the most frequently detected was blaZ (46.2%), and 32.3% of the isolates were positive for erm genes: ermC (21.5%) and ermB (10.8%). The most prevalent virulence gene was hla (100%), followed by hlb (84.9%) and sea (65.6%). These results show a low prevalence of antibiotic multidrug resistance in S. aureus isolates, even if the detection of selected antimicrobial resistance genes did not always correspond with the occurrence of phenotypic antibiotic resistance; the immune evasion cluster gene prevalence was quite low in the samples analyzed.

Assuntos

RESUMO

Non-agglutinating anti-Brucella abortus S45/20 antibodies were isolated and purified from sera of immunized cattle by means of immunoadsorption and ion-exchange chromatography (DEAE-Sephadex A-50). They corresponded to the IgG1 isotype as shown by immunoelectrophoresis using monospecific anti-IgG1 and anti-bovine gamma globulin sera. These antibodies failed to agglutinate the antigen. They were detected by the anti-bovine gamma globulin test, showing higher titres than those of agglutinating antibodies during the whole period of the experiment. Blood clearance of 131I-S45/20 in mice, was slower in those groups which had received non-agglutinating antibodies than in the control group.

Assuntos

RESUMO

Calves inoculated with Brucella abortus S45/20 produced, against surface antigens, non-agglutinating antibodies (NAAb) which were isolated and purified. A kinetic analysis was carried out of NAAb in antibody-dependent cell-mediated cytotoxicity (ADCC) using sheep red blood cells labelled with surface antigen from B. abortus S45/20 as target cells. Three parameters were examined: time of incubation, effector cell:target cell (E:T) ratio and NAAb dose. It was found that the NAAb were not able to mediate ADCC with bovine spleen cells.

Assuntos

RESUMO

Injection of different animal species with particulate T-dependent antigens induces the appearance of two antibody populations belonging to IgG class, one of them with agglutinating activity and the other lacking this capacity, that is, non-agglutinating. In this paper, 3 adult female Hereford were inoculated subcutaneously, fortnightly, four times, with 5 x 10(10) heat killed smooth S19 Brucella abortus cells. Blood samples were taken ten days after the last inoculation and were individually processed. Serum agglutinating titres against the homologous antigen and the Coombs test score were similar, indicating that nonagglutinating antibody titres directed against surface antigens of the smooth phase were not significant (Table 1). When sera were incubated with a suspension of Brucella abortus S45/20 (a rough strain) they showed poor agglutinating ability, but they contained non-agglutinating activity at high level, as determined by the anti-gamma-globulin test (Table 1). Similar results were obtained when the same sera were adsorbed with Brucella abortus S19 up to elimination of the antibodies directed against surface antigens, and then incubated with a suspension of strain 45/20 (Table 1). These antibodies were isolated from sera by immunoadsorption, using a thick suspension of S45/20 and then dissociated with glycine-CHl buffer 0.1M pH 3. These antibodies showed little agglutinating capacity for S45/20; however non-agglutinating antibodies were bound to the bacteria up to 1.5 micrograms g as demonstrated by Coombs test. Apart from the incomplete antibodies against external antigens of smooth Brucella abortus strains detected in long-term stimulated cattle, non-agglutinating antibodies with specificity for deeper antigens of the smooth bacteria were evidenced.(ABSTRACT TRUNCATED AT 250 WORDS)

Assuntos

RESUMO

Bovinos hembras de raza Hereford, inoculados con Brucella obortus cepa 19 en fase lisa, elaboraron anticuerpos no aglutinantes que se unieron específicamente a la cepa rugosa 45/20. Los sueros de estos animales, adsorbidos con B. abortus cepa 19 hasta eliminación de los anticuerpos dirigidos contra antígenos de superfície de la cepa lisa, mostraron contener una población no aglutinante de anticuerpos que se unieron a la cepa rugosa 45/20, siendo detectados mediante reacción de Cooms hasta un límite de 1,5 ug. Al margens de los anticuerpos incompletos producidos hacia antígenos externos de cepas lisas de B. abortus, se pone en evidencia este tipo de anticuerpos, con especificidad por antígenos más profundos que también estarían presentes en la superficie de la cepa rugosa. Estos anticuerpos, cuya participación en la depuración sanguínea y degradación del agente etiológico de la brucelosis bovina sería poco significativa, están siendo estudiados minuciosamente con el objeto de establecer la importancia que pudieran tener en el diagnóstico y pronóstico de brucelosis

Assuntos

RESUMO

Injection of different animal species with particulate T-dependent antigens induces the appearance of two antibody populations belonging to IgG class, one of them with agglutinating activity and the other lacking this capacity, that is, non-agglutinating. In this paper, 3 adult female Hereford were inoculated subcutaneously, fortnightly, four times, with 5 x 10(10) heat killed smooth S19 Brucella abortus cells. Blood samples were taken ten days after the last inoculation and were individually processed. Serum agglutinating titres against the homologous antigen and the Coombs test score were similar, indicating that nonagglutinating antibody titres directed against surface antigens of the smooth phase were not significant (Table 1). When sera were incubated with a suspension of Brucella abortus S45/20 (a rough strain) they showed poor agglutinating ability, but they contained non-agglutinating activity at high level, as determined by the anti-gamma-globulin test (Table 1). Similar results were obtained when the same sera were adsorbed with Brucella abortus S19 up to elimination of the antibodies directed against surface antigens, and then incubated with a suspension of strain 45/20 (Table 1). These antibodies were isolated from sera by immunoadsorption, using a thick suspension of S45/20 and then dissociated with glycine-CHl buffer 0.1M pH 3. These antibodies showed little agglutinating capacity for S45/20; however non-agglutinating antibodies were bound to the bacteria up to 1.5 micrograms g as demonstrated by Coombs test. Apart from the incomplete antibodies against external antigens of smooth Brucella abortus strains detected in long-term stimulated cattle, non-agglutinating antibodies with specificity for deeper antigens of the smooth bacteria were evidenced.(ABSTRACT TRUNCATED AT 250 WORDS)

RESUMO

Bovinos hembras de raza Hereford, inoculados con Brucella obortus cepa 19 en fase lisa, elaboraron anticuerpos no aglutinantes que se unieron específicamente a la cepa rugosa 45/20. Los sueros de estos animales, adsorbidos con B. abortus cepa 19 hasta eliminación de los anticuerpos dirigidos contra antígenos de superfície de la cepa lisa, mostraron contener una población no aglutinante de anticuerpos que se unieron a la cepa rugosa 45/20, siendo detectados mediante reacción de Cooms hasta un límite de 1,5 ug. Al margens de los anticuerpos incompletos producidos hacia antígenos externos de cepas lisas de B. abortus, se pone en evidencia este tipo de anticuerpos, con especificidad por antígenos más profundos que también estarían presentes en la superficie de la cepa rugosa. Estos anticuerpos, cuya participación en la depuración sanguínea y degradación del agente etiológico de la brucelosis bovina sería poco significativa, están siendo estudiados minuciosamente con el objeto de establecer la importancia que pudieran tener en el diagnóstico y pronóstico de brucelosis (AU)

Assuntos